System of phase transformation.



F. C. GREEN.

SYSTEM OF PHASE TRANSFORMATION.

APPLICATION FILED NOV. 21, 1911.

Patented Aug. 25, 1914.

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THE NORRIS PETERS C UNITED STATES PATENT OFFICE.

FRANK C. GREEN, OF PITTSFIELD, MASSACHUSETTS, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEVJ YORK.

SYSTEM OF PHASE TRANSFORMATION.

Application filed November 21, 1911.

To all whom it may concern.-

Be it known that I, FRANK C. GREEN, a citizen of the United States, residing at Pittsfield, county of Berkshire, State of Massachusetts, have invented certain new and useful Improvements in Systems of Phase Transformation, of which the following is a specification.

My invention relates to systems of distribution, especially to the producing of polyphase systems.

More particularly my invention relates to the method of, and the combination of devices for, producing a twelve-phase system from a three-phase system or vice versa.

It is at times desirable to derive a certain polyphase system from some different phase system. Thus in certain work, for example electrolytic, it is desirable to utilize a twelvephase system, whereas power is usually transmitted on a three-phase system. It is necessary, therefore, to provide means for deriving a symmetrical twelve-phase voltage from the three-phase voltage provided. Electrolytic work generally requires also a comparatively low voltage, a voltage differing greatly from the high voltage of the supply system or apparatus. This necessitates the use of transformers. The secondaries of these transformers should have an equal number of turns, since, where the step down is so great as is usual in this work, a very small number of turns only on the secondaries is required, perhaps but one or two turns, each turn having a very appreciable eflect. Generally then a difference in the number of turns on the secondaries requires the use of parts of complete turns. It is very difiicult to obtain the proper part of a complete turn in practice and a very appreciable error is hence very likely to creep in by the use of a part turn.

My invention in the form in which I have here disclosed it, contemplates the use of transformers, where desirable for changing the voltage and the phase, and also contemplates substantially equal voltages among the phases by the use of the same number of turns on the various smaller windings.

Figures 1 and 2 illustrate diagrammatically the relations between the voltages impressed on the primaries of transformers delta and Y connected and the voltages induced thereby in secondaries connected double delta; Fig. 3 shows diagrammati- Specification of Letters Patent.

Patented Aug. 25, 1914.

Serial No. 661,458.

cally the connections of transformers to obtain the voltage relations illustrated in Fig. 2. Fig. 1 illustrates diagrammatically the voltages induced in secondaries inductively related to primaries having the voltage re lations of Fig. 1 when the secondaries are diametrically connected; Fig. 5 illustrates dlagrammatically the connection of transformers to obtain the voltage relations illustrated in Fig. 4.

My invention as I have shown it here in deriving twelve phases from three phases involves the relative displacement of the voltages in delta and Y connections to a three-phase system. In Fig. 1 the solid lines illustrate diagrammatically the relations of the voltages of three windings connected in delta to a three-phase supply system; the dashed lines represent the relations of the voltages impressed by a three-phase system on windings Y connected. It will be apparent that there is a 30 degree relative displacement between the voltages impressed on the two sets of windings. To take advantage of this displacement to produce twelve phases from the three phases, transformers may be used. Thus in inductive relation to each of the primary windings 1, 2, 3 connected delta, and 4, 5, 6 connected Y, which receive impressed voltages related as shown in Fig. 1, are two secondary windings, 7 and 8, 9 and 10, 11 and 12, 13 and 14, 15 and 16, 17 and 18, respectively. The relations of the voltages induced in these various secondary windings are shown in Fig. 2, the various secondaries being double delta connected. The voltages induced by the delta connected primaries are shown in solid lines and those induced by the Y connected primaries by dashed lines. It will be apparent that the secondary windings of Fig. 3 may be regarded as parts of two six-phase systems or parts of four three-phase systems. The electro-motive forces of these two six phase systems are, however, relatively dison each primary winding when Y connected is less than the voltage impressed on each primary winding delta connected, it will be necessary, of course, presupposing the same number of turns on each 01' the twelve secondary windings, to have a lesser number of turns on the primaries Y connected than on the primaries delta connected. Since, however, in general work the primaries will be connected to the high voltage side, a difference in the number of turns can be more easily taken care of, since the addition of a part of a turn, or even of a small number of complete turns will have very little appreciable eiiect on the secondaries.

It will, of course, be understood that Fig. 3 may represent either two three-phase transformers, or six singlephase transformers, provided only that each primary is inductively related to two secondary windings.

A modification is shown in Figs. 4 and 5. Fig. i represents diagrammatically the relations of the voltages induced in secondary windings inductively related to primaries delta and Y connected respectively to a threephase system, when the secondaries are diametrically connected. For this diametrical connection there may be, of course, but a single secondary in inductive relation to each primary winding; this single secondary winding, however; may be regarded as two complete windings, or there may in fact be two complete separate secondary windings connected together. Thus Fig. 5 may be regarded as showing either two similar six phase systems, or four similar three phase systems, relatively displaced angularly. The connections of transformers to obtain these relations will be readily understood from the preceding description and Fig. 5. It is obvious that the combination of these systems will produce a symmetrical twelve phase system as represented in Fig. 4;.

What I claim as new and desire to secure by Letters Patent of the United States, is

1. The combination of two groups of windings, the members of each group being connected in double delta, and a group of windings inductively related to each of the first mentioned groups, the members of one of said last mentioned groups being connected in delta and the members of the other in Y.

2. The combination with a three-phase system of distribution, of two groups of transformers, one delta connected and the other Y connected thereto, the secondaries of each of the two groups being double delta connected.

In witness whereof, I have hereunto set my hand this 13 day of November, 1911.

FRANK C. GREEN. Witnesses MABELLE E. DENro, HERMAN O. VATJEN.

Copies of this patent may be obtained for five cents each, by addressing the Commissioner of Patents, Washington, D. C. 

